10 Unanswered Questions From Famous Movies That Are Still Killing Us
1. How Did Dignam Know Sullivan Was The Rat? - The Departed
The ending of The Departed is one of pure shock and adrenaline. After Colin Sullivan (Matt Damon) and Billy Costigan (Leonardo DiCaprio) had been chasing and trying to outwit each other, everything came to a head.
With almost everyone connected to the case or able to point to Sullivan as the rat dead, he was able to shift blame onto Trooper Barrigan (James Badge Dale), another that Costello had on the inside. He had seemingly escaped justice, at least from the police force, until he returned home to see Mark Wahlberg's Staff Sergeant Dignam waiting for him.
Dignam had been suspended earlier in the film and was almost forgotten about, until he returned to murder Sullivan right at the last. It's one of the most infamous movie endings we've had over the last two decades, but what it doesn't do is explain how exactly Dignam knew what Sullivan had done.
It appeared that everything had been wrapped up in a neat little bow for Colin, particularly as there wasn't anyone left alive who had proof of his connection to Frank Costello. So, how did Dignam know? There are theories certainly, revolving around Vera Farmiga's Madolyn Madden, or potentially that Dignam himself was a rat, the former of the two being the most believable, but there is no solid answer, and likely never will be.